The invention relates to improvement in the flame-retardant character of polyurethane foams and specifically hydrophilic foams based on polyurethanes having a polyoxyethylene backbone. Such foams are well known in the art. The object of the invention is to increase the flame-retardancy of such foams by incorporating various additives which are believed to strengthen the char evolved during combustion.
A relevant prior art reference is H. Z. Vandersall, Journal of Fire and Flammability, 279 (1971) describing the state of the art in intumescent paint chemistry. At pages 101 and 104 of this article, formulations employing carbonizable compounds such as starch are described.
Flame retardance additives have been described in U.S. Pat. No. 3,455,850 (porous filler coated with ammonium polyphosphate); U.S. Pat. No. 3,629,162 (whey); U.S. Pat. No. ,3,639,307 (fumaric acid); U.S. Pat. No. 3,826,762 (inert filler, halogen source, phosphorous-containing compound); U.S. Pat. No. 3,865,760 (alumina trihydrate plus source of calcium or borate radicals); U.S. Pat. No. 3,897,372 (melamine - mentioned above); U.S. Pat. No. 3,909,464 (antimony oxide, alumina trihydrate, polyhalogenated aromatic compound); and U.S. Pat. No. 3,810,851 (alumina trihydrate or antimony trioxide in PVC polyurethane foams). U.S. Pat. Nos. 3,021,290 and 3,051,601 describe the use of talc or wood cellulose to provide flexible polyurethane foams having improved load bearing capacity. U.S. Pat. No. 3,573,234 describes the use of sodium carboxymethylcellulose and related compounds to increase the hydrophilic character of polyurethane foams.